Vaporization system having improved feed liquid recirculating means



April 2, 1968 I c. A. E. BEURTHERET 3,375,363

VAPORIZATION SYSTEM HAVING IMPROVED FEED V LIQUID mzcmcum'rme mms Filed Aug. 15, 1966 19 &

5 sheets sheet l 4 gg m April 2, 1968 c. A. E. BEURTHERET 3,375,868

VAPORIZATION SYSTEM HAVING IMPROVED FEED LIQUID RECIRCULATING MEANS Filed Aug. 15, 1966 3 Sheets5heet April 2, 1968 c A E. BEURTHERET 3,375,868

VAPORIZATIbN SYSTEM HAVING IMPROVED FEED LIQUID RECIRCULATING MEANS Filed Aug. 15, 1966 3 Sheets-Sheet 5 United States Patent O 21 Claims. (in. 165-105) This invention has as a broad object the provision of an improved liquid feed arrangement for vaporization systems, especially of the closed-circuit recirculatory type, in which a liquid is made to vaporize partly in a boiler by a heat-dissipating source, the vapour is passed to a condenser forming part of a recirculating feed circuit, and the condensed liquid is returned from the condenser to the boiler for renewed vaporization.

The chief applicability of the invention lies in the field of vaporization cooling systems of the type used for cooling high-power electron discharge devices in radio transmitter stations, industrial alternating power plants, and similar installations. The invention will, ac-

cordingly, be disclosed with particular reference to this field of application.

An important object of the invention is the provision of an improved liquid feed arrangement for a closedcircuit vaporization system, in which novel use is made of a phenomenon known as the annular mode of flow of a two-phase fluid through a conduit in order to elevate liquid from a \boiler to an overhead condenser without having to provide a pump or any other kind of liquid circulating device for that purpose.

In closed-circuit vaporization cooling systems for power electron tubes and the like, the electron tube to be cooled is usually arranged in upside-down position, with its heated section, such as the anode or collector heated by the impact of bombarding electrons against its internal surface, being immersed in a body of liquid con tained in a boiler tank. The liquid vaporizes partly through contact with the hot outer surface of the anode, and the vapour collects in a vapour collector provided at the top of the boiler tank. This vapour is discharged through a vapour discharge pipe to the inlet of a condenser, and the condensed liquid is returned from the condenser outlet, by way of a liquid feed line, to an inlet provided at the bottom of the boiler tank.

For safe and eflicient operation of the electron tube, it is important that the level of the boiling liquid in the tank shall at all times be maintained at a constant level. To ensure this, one of two chief arrangements have conventionally been used for the fluid circulating circuit.

In a first, so-called static, lay-out, the vapour discharge line extends upward from the vapour collector at the top of the boiler and the vapour flows upward through this line to the condenser by the action of the pressure generated in the boiler. The condensed liquid flows down by gravity from the condenser into a constant-level reservoir and thence into the boiler inlet. The constant level of liquid in the reservoir determines the constant level of liquid in the boiler tank. This lay-out is advantageous in that it does not require a pump or other source of power to circulate the fluid around the system, since the vapour rises into the condenser by its own pressure and the condensate drops into the boiler by its own weight. However, the arrangement has serious drawbacks. First, the level of the liquid in the boiler in only maintained ap proximately constant at the reference level obtaining in the reservoir, and in practice it fluctuates considerably around that reference level in accordance with fluctuations in the power output of the tube. To prevent such 3,375,858 Patented Apr. 2, 1968 level fluctuations from exceeding permissible limits, the pressure drop and flow resistance through the system must be kept very low. Separator means must be provided for positively preventing the entrainment of any liquid with the vapour into the vapour discharge pipe, since this would cause obstructions liable to result in dangerous variations in level in the boiler tank. Another inconvenience of this static layout is the fact that the rising vapour discharge pipe connecting with. the top of the boiler t-ank interferes with the arrangement of the electrical circuitry that is normally connected with the input and output leads of the inverted electron tube, which project upward from the top of the boiler tank.

The second above-mentioned arrangement conventionally used may be termed the overflow lay-out. The boiler tank is provided with an overflow weir at an elevation corresponding to the desired constant level of liquid to be maintained in the tank. A pump is provided to deliver liquid from the condenser into the boiler tank at a flow rate consistently higher than the rate of vaporization in the boiler, so as to ensure that non-vaporized liquid is continuously overflowing and thus positively maintains the level at the prescribed height. The overflowing liquid is returned to the pump inlet, while the vapour is discharged from the collector at the top of the boiler by way of a discharge line which may include a downgoing initial leg so as to receive the overflowing liquid together with the vapour, a liquid/vapour separator being provided at the lowermost point of the vapour discharge line. This arrangement has important advantages, chiefly including the fact that the liquid level in the boiler tank is held strictly constant regardless of power fluctuations. However, it necessitates the use of a pump, which is obviously troublesome.

It is a specific object of this invention to provide a vaporization cooling system of the overflow type just specified, in which the use of a pump or other ancillary equipment for recirculating the non-vaporized liquid around the system is obviated.

As earlier indicated herein, the invention relies on the annular mode of flowiof a two-phase (liquid-vapour) fluid system, to elevate the non-vaporized liquid together with the vapour discharged from the boiler up through a rising vapour-discharge line, to the condenser.

It has been known for some years that when a mixture of vapour and entrained liquid is passed through a rising conduit, then if the linear flow velocity of the vapour is increased above a certain critical value, a socalled annular flow regime becomes established in which the liquid segregates from the vapour as an annular film clinging to the wall of the conduit while the vapour flows axially of the conduit. It is found that the axial vapour core is capable of entraining the annular liquid film by friction,

. so that considerable amounts of liquid are able to climb up a rising conduit without requiring the expenditure of any ancillary power. In the case of water, the critical velocity above which this annular flow mode sets in is found to be about 30 meters per second. According to the invention, therefore, the vapour discharge pipe in a recirculatory vaporization system of the type referred to above, is provided with a flow section area so small that under the operating conditions utilized the vapour discharged from the boiler is constrained to assume a velocity greater than the critical velocity for annular flow, e.g. not less than about 35 meters/second in the case of steam.The vapour is then able to elevate the non-vaporized liquid overflowing from the overflow weir of the boiler without pumping. Where the fluid is water and under the conditions normally prevailing in vaporization cooling systems for power electron discharge devices, the flow section area of said rising vapour discharge line should be smaller than about 0.2 square centimeter per kilowatt power dissipated by the device, in order for the desired critical velocity to be exceeded. Preferably, said section area is less than about 0.1 cm. per kilowatt average power dissipated under steady operating conditions. The vapour discharge pipe includes a downgoing initial pipe section or leg extending from the boiler so as to receive both the vapour from the vapour collector at the top of the boiler, and the liquid overflowing from the weir. This downgoing leg connects with the main, upgoing leg of the vapour discharge pipe (in which the annular flow mode becomes established) by way of a connecting section of large curvature radius.

In a feed system according to the invention, the energy for raising the liquid is taken from the kinetic energy of the vapour by way of the frictional coupling present between the vapour core and the annular liquid film in the rising vapour discharge line. The kinetic energy of the vapour is, of course, proportional to the static pressure of the vapour developed in the boiler. This static pressure is balanced, in the system of the invention, by the static pressure of a liquid column present in the liquid feed line extending from the condenser outlet to the boiler feed inlet. The height of this liquid column in the feed line can be easily varied by varying the total amount of liquid introduced into the closed system. The liquid column provided must be of a height sufficient to balance the pressure required to elevate the entrained water by annular flow effect as just stated above, plus the pressure drop through the system, as determined by the flow sections in various parts of the closed-circuit system. In this Way, selection of the total amount of fiuid introduced into the system, for a given dimensioning of the latter, provides a means of readily controlling the relative amount of excess overflow liquid recirculated throng the system with the entraining vapour.

Another possibility afforded by the invention in this respect is to provide the aforementioned static column of feed liquid ahead of the boiler input high enough, in excess of the height strictly required to produce the desired entrainment of liquid by annular flow, so that it will serve to balance additional pressure drops that may be introduced into the feed liquid line by passing the feed liquid in heat-abstracting relation with ancillary components to be cooled, e.g. a UHF inductance coil associated with the electron discharge device.

Further objects and features of the invention will become apparent from the ensuing description of exemplary embodiments, made with reference to the accompanying schematic drawings, wherein:

FIG. 1 illustrates a vaporization cooling system according to an embodiment of the invention, as applied to a high-power electron tube;

FIG. 2 is a large-scale perspective view of part of the upgoing leg of the vapour discharge pipe of the system shown in FIG. 1, illustrating a helical deflector element positioned in the conduit to promote the establishment of annular flow conditions therein;

FIG. 3 is a large-scale view in elevation of part of the vapour discharge pipe of the same system, equipped with a device according to a modification of the invention, for automatically draining said pipe on shut-down of the system and re-entraining the drained liquid on resumption of operation.

FIG. 4 is a large-scale view of part of the system according to another modification, wherein the vapour discharge pipe includes more than one upgoing legs of different cross section in parallel; and

FIG. 5 is a general view of a system generally similar to FIG. 1 but including certain additional modifications.

The electron tube cooling system shown in FIG. 1 includes a boiler tank or shell 1 in which the electron tube 2 to be cooled is immersed in an inverted position, the boiler shell 1 being connected with u condenser heatcxchanger unit 17 by way of a vapour conduit 3 connecting with the top of the .boiler 1 and a liquid conduit 5 connecting with the bottom of the boiler. The boiler shell 1 contains a body of vaporizable liquid 6, e.g. water, the upper free surface level of which, designated 7, is determined by an overflow weir 8 provided at the top of boiler shell 1, and discharging into the inlet opening 9 of the vapour conduit 3, which inlet opening connects with the base of a vapour collector box 10 constituting the top of the boiler shell 1. The shell 1 contains an annular wall or deflector 11 spaced both from the outer surface of the tube 2 and the inner surface of shell 1 and open at its upper and lower ends, said annular bafile serving to promote thermosyphon e'lfect in the liquid in that it guides the vapour formed adjacent the hot wall of tube 2 in an upward direction and guides the stream of cooling liquid adjacent the outer wall of boiler shell 1 peripherally in the downward direction.

The electron tube 2 to be cooled may be any high-powered tube requiring energetic cooling, and is shown as having its hot anode section 12 provided externally with heat-dissipating protuberances 13 so shaped and dimensioned as to ensure in operation the establishment of stable temperature gradients along their side surfaces whereby relatively very high temperatures can be attained at the tube surface without danger of local burnout. Anisotherm heat-dissipating formations of this type have been disclosed in a number of the applicants earlier patents and other publications and are now in world-wide commercial use under the trade name Vapotron in connection with high-powered electron discharge devices. Said patents and application include: United States Patents 2,935,305; 3,046,428; 2,969,957; 3,235,004; 3,196,936 and United States patent application Ser. No. 512,090, filed Dec. 7, 1965.

The steam conduit 3 includes a descending leg 14 con necting with the boiler collector 19 as earlier described, followed by a major rising leg 15 connecting with the upper end of condenser 17'. The legs 14 and 15 connect by way of the downwardly convex knee section 16 of large radius.

The water conduit 5 connects the lower outlet end of condenser 17 with the bottom of the boiler shell or tank 1 and also in this embodiment includes two vertical legs of unequal extent interconnected by a large-radius bottom knee section as shown. A vent tube 19 is preferably connected with water conduits 5 near its upper end. Since it is customary in installations of the type described to maintain the entire boiler unit in contact with the copper anode wall 12 at the high electric potential of the anode, means are preferably provided for electrically insulating the boiler unit from the remainder of the cooling system. As shown, for this purpose each of the conduits 3 and 5 includes an inner end section connecting with the boiler, as shown at 20 and 21 respectively, which is made of insulating material. The outer sections of said conduits 3 and 5 can then be grounded, as indicated.

The condenser 17 may be any suitable heat exchanger of conventional type and is here shown as being cooled by an external air draft created by a fan 18 schematically illustrated.

The steam conduit 3 or at least the rising leg 15 of it, is provided with a relatively narrow internal diameter so as to impart to the steam passing through it from the boiler collector 10 a sufiiciently high linear velocity, e.g. higher than about 35 meters/ sec.

In operation, the anode wall 12 of tube 2 is carried to a high surface temperature owing to the heat supplied to it internally by electron bombardment: of the inner anode surface not shown during the normal operation of the electron tube. The water 6 is carried to ebullition on contact with the anode wall 12 and the generated steam rises as bubbles through the body of water and is discharged into the upper steam collector 10. This vapour, together with some entrained liquid water, is discharged through the opening 9 into the vapour conduit 3, in which the liquid-vapour mixture takes on a high linear flow velocity of at least 30 meters/sec. and preferably somewhat higher owing to the relatively small inner flow section of pipe 3. At this high flow velocity, the steam and liquid water are caused to separate from each other after a short distance of travel through pipe 3, and the socalled annular flow earlier described becomes established. In this mode of flow, the steam flows almost exclusively though the central or axial region of pipe 3 and the water assumes the form of an annular sheath surrounding the steam adjacent the wall of the pipe, and adhering to the wall surface. The axial stream of steam at high velocity entrains the surrounding sheath of liquid by friction, and carries it up the pipe 3 into the upper inlet of condenser 17. Here the steam condenses, and the liquid condensate, plus the liquid water that Was carried into the condense-r by the steam as just described, flows by gravity down the water pipe 5. In the downpipe 5, the water from condenser 17 settles to a certain level 22 which is substantially higher than the free level 7 in boiler 1 as determined by the overflow weir 8. In the steady state, the height h of the water level in pipe 5 above the level 7 in the boiler is such that the weight of the water column balances the pressure required in the boiler to force the steam issuing into pipe 3 to assume the high flow velocity indicated, plus any pressure drops through the water feed system. It is demonstrable that the elevation 12 is substantially proportional to the product of the steam velocity squared and the total length of the steam conduit 3. The elevation h can be readily controlled by adjusting the total mass of fluid contained in the system since, when said mass is increased, then assuming a constant rate of vaporization in the boiler, the rate of mass flow of liquid transiting through the boiler and passing in the liquid state into the condenser must necessarily increase correspondingly. In practice, over a Wide range of power ratings of the tubes to be cooled, and assuming reasonable values for the parameters of the system, it is generally found satisfactory to maintain the elevation 11 at a value of approximately one meter. This may include allowance for any additional pressure drops, primarily the flow resistance in the liquid pipe 5 and especially the insulating section 21 of it.

When the operation of the electron tube is arrested, vaporization in the boiler of course ceases, and the flow of steam through pipe 3 also ceases. The dynamic pressure balance conditions above described are then superseded by a normal hydrostatic balance condition in which the water level in water pipe 5 is the same as the overflow level 7 in the boiler. As a result, the excess liquid in the column of elevation 11 flows into the boiler and a corresponding amount of liquid is emptied from the boiler into the knee section 16 of steam pipe 3. This is usually unobjectionable, since it is found that on resumption of operation the steam initially generated in the boiler first bubbles through the said body of water that has collected in the knee 16, and after a short time builds up sufficient speed to initiate the annular flow conditions and promptly takes up the said collected water and carries up into the condenser.

As will be apparent from the description just given, the cooling system of FIG. 1 ensures the desired circulation of liquid and vapour around the closed circuit comprising the boiler and condenser, while maintaining a strictly constant level in the boiler by overflow action, and achieves this result without the use of a pump as was heretofore required. No separator is necessary either.

As earlier indicated, the annular flow regime utilized to achieve these purposes in the invention is found to set in when the linear flow velocity of the vapour in a two-phase mixture through a conduit exceeds a critical velocity. This critical velocity, where the fluid is water, is about 30 meters per second. The flow section area of the rising leg of the vapour discharge line should therefore, according to the invention be made smaller than the value for which this 6 critical velocity will be exceeded, and preferably, such as to impart to the water vapour a linear flow velocity not less than about meters per second.

The flow velocity V of a fluid through a conduit of flow section area sis given by the equation where q is the volume flow rate. In vaporization cooling ysterns of the kind to which the invention relates, the mass flow rate of water vapour required is generally considered to be about 1 kilogram per minute per kilowatts power dissipated by the electron tube 2. In terms of volume, this mass of vapour represents 1700 cubic decimeters of steam per minute and per 40 kV-L, or about 707 cubic centimeters per second and per kilowatt. The equation just written then indicates that the flow section area s should be less than 707:350() or about 0.2 cm. per kilowatt power to be dissipated. Preferably, the section area is selected at a value not greater than about 0.1 cm? per kilowatt average power dissipated by the electron tube under steady-state operating conditions, so that in these conditions the flow velocity of the vapour will be not less than about meters per second. This will provide a useful safety margin ensuring that the vapour velocity will not drop to a value below the critical value required for annular flow, even in case of any reasonable momentary drops in tube output, for accidental or deliberate causes. Actually, the flow velocity of the vapour through the upgoing vapour discharge pipe section 15 will at any time be proportionate to the heat dissipating rate, and can well eX- ceed meters per second or more.

By the means of the invention, the liquid can be ele vated to relatively large heights without the use of any ancillary power. Thus, in the system of FIG. 1, the condenser 17 may be disposed at a height of e.g. 5 meters above the level of the overflow weir in boiler 1, and the entrained water will be reliably raised to that height by the annular flow through pipe section 15 dimensioned as indicated above, using a liquid column h in the liquid feed pipe 5, but not substantially higher than about 1 meter.

The liquid feed pipe 5 has a flow section area that is preferably substantially smaller than that of the upgoing leg 15 of the vapour discharge pipe 3.

It will be understood that the provision of the down going initial section 14 of the vapour discharge pipe, which connects with the rising leg 15 by way of a largeradius connecting section 16 as described above, is not only convenient because it provides a natural arrangement for receiving the overflowing liquid from overflow weir 8 together with the vapour from the vapour collector 10 of the boiler, as well as avoiding interference with the electric circuitry (not shown) that would normally be connected with the upwardly projecting inputs and outputs of the electron tube 2. The said downgoing leg 14 of the vapour discharge pipe has the further important function of imparting a high initial velocity to said overflowing liquid, with the assistance of gravity, so that the entrained liquid will more rapidly and smoothly assume a flow velocity corresponding to that of the vapour in which it is entrained. The establishment of the. desired annular flow regime in the upgoing leg 15 of the vapour discharge pipe is thus made very much easier and smoother.

According to a secondary feature of the invention, the establishment of the requisite annular flow regime in the rising pipe section 15, can be further facilitated and improved by using an expedient now to be described with reference to FIG. 2.

As shown in FIG. 2, the rising leg 15 of the steam conduit 3 in FIG. 1, is provided internally with a helical deflector element 23 fixedly mounted in the conduit in en gagement with its inner wall surface. A convenient way of providing such a helical deflector is to use a wire of a suitable resilient and non corrodable metal, preliminarily coil the wire around a drum of substantially larger diameter that the inner diameter of the conduit in which it is to be mounted, say 1 /2 to 3 times said inner diameter, so as to form a coil spring having said increased diameter, and then draw the resulting coil through the conduit 15. No further means for securing the wire in place are found necessary. In operation, such a helical deflector when inserted in a riser pipe imparts a whirling motion to the fluid flowing through the pipe, and the centrifugal forces thus created tend to throw the heavier liquid radially outward against the peripheral wall of the conduit, thereby promoting the establishment of the desired annular flow mode. While such a helical deflector does not sensibly diminish the minimum flow velocity at which the annular flow will set in, it does notably reduce the transitional period required for such annular flow to become firmly established initially. The arrangement just described is, therefore, especially useful in systems that are subject to frequent stoppages and/or large fluctuations in heat dissipation rate in service.

As earlier indicated, after .a shutdown period a body of liquid collects in the lowermost section 16 of the vapour pipe 3, this liquid representing the excess that was stored as the liquid column of elevation h in the liquid conduit under the dynamic balance conditions that prevailed during operation. As mentioned above, this collected water is soon carried away by the vapour stream after vaporization has resumed in the boiler. However, in some installations in which a relatively large excess of liquid is desired in operation, or should it be desired for other reasons to reduce the time required to establish annular flow conditions after shutdown, the device shown in FIG. 3 may be used. The lowermost bend section 16 of the vapour pipe 3 has a small sealed tank 24 mounted below it and connected with said pipe section by way of two vertical connecting tubes 25 and 26. Tube 25 connects with the lower part of the wall of pipe 3 and its extremity 27 connecting with said pipe is directed preferably in the same direction as the flow of steam through pipe 3, which flow direction is indicated by arrows. The other connecting tube 26 has its upper end connecting with the upper part of the section of pipe 3 and is directed at its connecting extremity 28 in a direction counter to that of vapour flow in the pipe 3. Tube 26 has its lower end connecting with the top of sealed tank 24 while tube 25 has its lower end opening near the bottom of said tank. This device operates as follows.

On shutdown, the limited amount of liquid that flows into the bottom bend 16' from column 11 as earlier explained, drops by gravity into the tank 24 through tube 25. When the system is started back in operation, the vapour generated in the boiler can flow freely through the pipe 3 without being impeded by liquid therein, so that it very quickly attains the prescribed flow velocity at which annular flow sets in. It will be noticed that due to the different orientations of the connecting sections 27 and 28 of tubes 25 and 26 with pipe 3, they constitute in effect a differential pressure takeoff of a well-known type used in Pitot airspeed meters. That is, tube 26 whose connecting section 28 is directed against the flow of vapour, senses a dynamic pressure which is substantially higher than the static pressure sensed by tube 25 whose connection 27 is directed in the same sense as the vapour flow. As the vapour flow velocity in pipe 3 increases, the pressure differential across the two tubes 25 and 26 rises correspondingly, and when said flow velocity is high enough, the over-pressure sensed by dynamic pressure take-off 28 becomes great enough to act on the surface of the liquid in tank 24 so as to force the body of liquid collected therein up through tube 25 and back into the pipe 3, where it is taken up by the now rapidly flowing vapour steam to be carried off to the condenser as already described.

FIG. 4 illustrates a modification which is of special value in cases where the apparatus to be cooled is subject to periods of operation at widely differing power rates. This may occur for instance in the case of tubes in certain communication systems which are required to remain for long periods of time in an expectant condition with the cathode heated and little or no power ap plied to the anode, as well as in various other installations involving prolonged idling periods in service. As shown, the vapour pipe 3 has a branch pipe 29 of substantially smaller diameter branching off from it at a point somewhat ahead of the lower bend 16 therein, the branch pipe 25 connecting with the descending pipe section 14 by way of another bend of suitably large radius. Branch pipe 29 at its upper end connects with the condenser inlet, not shown in this figure. In this modification, the separator device of FIG. 3 is not used, so that after a shutdown period a body of liquid 16 has collected in the bend 16 of main vapour pipe 3. During an idling period of operation when the rate of vaporization in the boiler is greatly reduced, the small amount of vapor is unable to pass through the body of liquid 16 and is forced to flow entirely through the small diameter branch line 29, in which it assumes the critical flow velocity required for annular flow, thereby ensuring the desired operation at the low operating rate considered. When normal operation begins, the rate of vaporization in the boiler is considerably increased, and the resulting vapour pressure in the descending or inlet conduit section 14 becomes so great that it cannot all be discharged through the narrow pipe 29, which has now become the greater obstacle to vapour flow. The high pressure vapour therefore bubbles through the liquid 51 until it has reached the critical velocity for annular flow in the main riser leg 15, whereupon the collected liquid 51 is carried off as earlier described. Thus proper annular-flow operation is ensured both normal and reduced vaporization rates. Satisfactory results have been obtained with a branch leg 29 having a diameter somewhat less than one fifth the diameter of the main riser leg 15.

It will be understood that the idea of having more than one risepipes of different diameters branching off from the boiler vapour outlet and leading to the condenser, as shown in FIG. 4, in order to ensure the establishment of the desired annular-flow mode of fluid flow under different rates of vaporization in the boiler, does not necessarily rely on using the body of liquid 51 collecting in the bottom of the vapour conduit in order to effect the automatic switching of the vapour flow from one to another branch conduit, as just described with reference to FIG. 4. Instead, such switching may readily be effected by means of suitable valving, which may be controlled manually or preferably automatically through any suitable means responsive to the rate of vaporization in the boiler or the steam pressure or any equivalent factor, as will be easily understood by those familiar with the art.

FIG. 5 illustrates an embodiment of the invention which is essentially similar to that shown in FIG. 1 but includes a number of ancillary devices which may improve the operation. It is to be understood that the various improvements shown in FIG. 5 over the basic system are not necessarily applied simultaneously as here shown by way of example, but are applicable in any combinat1on.

A first improvement shown in FIG. 5 involves the construction of the boiler 1. In the simple form of boiler shown in FIG. 1, it can sometimes happen at the higher heat dissipation rates that the vigorous tboiling creates such intense turbulence that an excessive amount of liquid is ejected over the overflow weir and entrained with the vapour, at a rate higher than the desired rate as determined by the elevation h prescribed for the liquid column. The level of liquid in boiler 1 can then at times become depleted with a consequent danger of damage to the electron tube 1. This is avoided by using the type of boiler shown in FIG. 5, which includes a liquid-vapour sepa- 9 rator device generally similar to that disclosed in applicants US. Patent 2,935,306. The outer shell 1 of the boiler connects with the downgoing leg 14 of the vapour conduit 3 by an opening 34 at the bottom of the shell. An inner boiler shell 32 spaced from the outer shell 1 and from the anode wall 13 of tube 2 and mounted in.

place through means not shown, contains the boiling liquid which is supplied thereto through an inlet 33 at the bottom thereof. The upper edge of the inner shell 32 constitutes an annular overflow weir for discharge of the water into the vapour outlet 34. The outer shell 1 at its top is formed with a semi-toroidal shape as shown to provide an annular vapour collector. The separator referred to above comprises a cylindrical deflector wall 30 having its lower end dipping into the body of water in the inner shell 32, and a ring of generally radial, angularly spaced separator vanes 31 connecting the upper end of deflector wall 30 with the inner edge of the vapour collector. The baflles or vanes 31 are curved at an upwardinward angle such as to deflect back into the inner shell and into the hot inner region thereof the major part of the water that may tend to be splashed out by the aforementioned turbulence, whereas the steam is allowed to pass out freely through the spaces between said vanes. The relatively cool liquid in the outer annular region surrounding the wall 30 and adjacent to the overflow weir is comparatively quiescent, so that it does not tend to overflow into the vapour outlet 34 at a rate higher than the prescribed rate determined by the height of the liquid column h as earlier described.

The bottom bend 16 of the steam pipe 3 is equipped with the liquid collecting device including sealed tank 24 and connecting tubes 25 and 26, as described with reference to FIG. 3. The collector tank 24 is herein provided with a liquid level sensing device 50 for a purpose later described.

In this embodiment Water separator means are associated with the upper part of the riser pipe 3 and comprise a separator casing 36 tightly surrounding a perforated section 37 of the rising leg 15 of the steam pipe. This perforated pipe section 37 is internally fitted with a helical deflector strip or wire 38, similar to that described wtih reference to FIG. 2. Helical deflector 38 may, in fact, actually form part of a helical deflector of the type described in reference to that figure and extending over a major length of said rising leg 15. The separator casing 36 has a lower outlet leading into a cooling heat-exchanger 17a cooled by an external air draft from fan 40, the outlet of cooler 17a delivering directly into the water pipe 5. It will be understood that the water carried up with the steam through pipe 3 is discharged outward through the perforated pipe section 38 by the centrifugal force imparted to it by the helical deflector 37, and is then returned, after cooling in cooler 17a, to the water feed pipe for delivery to the boiler together with the condensate flowing from the condenser, herein designated 17b. Separation of the Water-cooling and steam-condensing functions, as achieved with the arrangement just described, improves the efficiency and is further advantageous in that it makes possible a convenient spatial separation of the water cooler 17a and condenser 17b. The cooler 17a may desirably be located adjacent to the radio transmitter or other system of which the device 2 to be cooled forms part, whereas the condenser 17b may be positioned at some other suitable point, e.g. under the roof of the building.

Means are provided in this embodiment for preventing the elevation of the liquid column in pipe from exceeding a determined upper limit, indicated as H, somewhat higher than the nominal value h prescribed for said column. For this purpose there is provided an overflow pipe 41 connecting with a side of pipe 5 at the desired level, and leading into a collecting tank 42 provided with a level gauge 43, e.g. of the simple visual type. Tank 42 is connected by a line 44 with a lower point of the liquid feed line 5, and a normally closed manual valve 45 interposed in line 44 may be opened when desired to reinject make-up liquid to replenish the system when depleted after prolonged operation or for other reasons.

Preferably, the liquid pipe 5 is provided just below the overflow pipe 41 with an enlargement constituting a small storage reservoir 46, which serves to take up rapid fluctuations in the level of water around the prescribed elevation h and prevent immediate overflow. The reservoir 46 is arranged so that the liquid level 2-2 when at the prescribed nominal elevation h reaches substantially to mid height thereof.

The system is further shown provided with a number of level sensing probes, which include the probe 50 earlier mentioned as associated with the bottom collector tank 24, and two further probes 48 and 49 connected to spaced points of the liquid feed pipe 5, probe 48 being somewhat below the nominal elevation h and probe 49 at a level just below the prescribed liquid level 7 in the boiler. Each of the probes 48, 49, 50 is desirably of the type wherein a normally open pair of contacts projecting into the pipe or tank With which the probe is associated, is adapted to be shorted by the liquid when it rises to the corresponding level. The level sensing contacts (or other electric level sensers used, such as capacitive sensers), may be interconnected in any desired monitoring and safety circuits. In one suitable safety arrangement, the level sensers are so interconnected with the power supply circuits of the electron discharge tube 2 to be cooled, that power cannot be applied to the tube anode unless both probes 49 and 50 are sensing liquid at the corresponding levels, and further, that the power will be automatically out off after a predetermined period of time has elapsed from the instant of power application, if the probe 48 has not indicated that the liquid has risen to the associated level.

One final improvement indicated in FIG. 5 lies in the fact that an inductance coil 47 forming part of the anode circuit of tube 2 is interposed in the liquid feed line, as shown, to be cooled thereby. For this purpose coil 47 comprises an appropriate number of turns of a tubular conductor having one end connected with the bottom inlet 33 of inner boiler shell 32 and its other end connected with the insulating pipe section 21 connecting with the descending vertical section '5 of the liquid feed pipe. This latter is earthed as in the embodiment of FIG. 1.

Among the many modifications that may be introduced into the described apparatus Without the scope of the invention being exceeded, are those relating to simplifications that are made possible in cases where a plurality of electron tubes, preferably having substantially similar power ratings, are to be cooled. The cooling circuits for the tubes may then have certain parts in common, e.g. the condenser water-cooler, if used, and part or whole of the water supply line 5 and its ancillary equipment. The tubes may be arranged in separate boilers fed in parallel from pipe 5, or several tubes may be arranged in a common boiler of appropriate construction.

What I claim is:

1. A vaporization system comprising:

a boiler having a body of vaporizable liquid therein .and including an inlet for feed liquid; a heat dissipating source in the boiler immersed in said liquid whereby the liquid is partly vaporized; overflow means associated with the boiler to maintain the free surface of said liquid at a constant level; and

a recirculatory feed system for said liquid comprising:

a condenser positioned at an overhead level substantially higher than said constant liquid level, and having an inlet and an outlet;

a liquid feed pipe connected to the outlet of the 11 condenser and connected to the inlet of the boiler; and a vapour discharge pipe connected to said boiler so as to receive therefrom vapor together with non-vaporized liquid overflowing from said overflow means, and including an upgoing leg connected to the inlet of the condenser; means to pump to the condenser, by the annular flow effect, the liquid spilled over the overflow means into the vapor discharge pipe by the boiling process comprising:

suflicient amount of liquid in the system so that the height of the column of liquid above the level in the boiler is suflicient to balance the pressure drop through the boiler and the pressure drop required to elevate the water entrained by the annular flow effect, the upgoing leg of the vapor discharge pipe having a flow sectional area small enough to maintain the velocity of the vapor in the upgoing leg at least at the critical velocity for the liquid, and a downgoing leg connecting with the overflow means and with said upgoing leg.

2. A system according to claim 1, wherein said vapor discharge pipe includes said downgoing leg connected to the boiler and connected to said upgoing leg by way of a large radius connecting section.

3. A system according to claim 1, wherein said liquid is water and said flow section area of the upgoing leg of the vapor discharge pipe has a value not substantially larger than that corresponding to a linear vapor flow velocity of about 35 meters per second.

4. A system according to claim 1, wherein said liquid is water and said flow section area of the upgoing leg of the vapor discharge pipe is not substantially greater than about 0.2 cm. per kilowatt power dissipated by said source.

5. A system according to claim 1, wherein said liquid is water and said flow section area of the upgoing leg of the vapor discharge pipe is not substantially greater than about 0.1 cm. per kilowatt power dissipated by said source in steady operation.

6. A system according to claim 1, wherein said liquid feed pipe has a flow section area smaller than the flow section area of said upgoing leg of the vapor discharge pipe.

7. A system according to claim 1, including a helical deflector element mounted in said upgoing leg of the vapor discharge pipe adjacent to the inner wall surface thereof to promote establishment of said annular flow mode.

-8. A system according to claim 1, wherein said vapor discharge pipe includes at least one auxiliary upgoing leg extending to said condenser inlet in parallel with said first-mentioned upgoing leg, the auxiliary upgoing leg having a flow section area substantially smaller than that of said first-mentioned upgoing leg.

9. A system according to claim 1, wherein the amount of said liquid in the system is so predetermined that a liquid column of substantial height is maintained in said liquid feed pipe above the boiler inlet in operation.

10. .A system according to claim 9, including an overflow pipe connected to a point of the liquid feed pipe at an elevation somewhat higher than the desired height of said liquid column, a storage tank fed from said overflow pipe and a liquid recovery pipe connecting said storage tank with a point of the liquid feed pipe at a lower elevation, and valve means associated with said liquid recovery pipe.

11. A system according to claim 9, including a storage reservoir chamber communicating with the liquid feed pipe at an elevation slightly lower than said maximum desired height of the liquid column.

12. A system according to claim 1, including a liquid vapor separator connected in said vapor discharge pipe somewhat below the connection of the upgoing leg thereof with the vapor condenser inlet, said separator having an outlet for separated liquid, and a branch line connecting said separated liquid outlet with said liquid feed pipe, including cooling means for the separated liquid in said branch line.

13. A system according to claim 1, wherein said heat dissipating source is formed with heat dissipating projections on an outer surface thereof contacting said liquid, which projections are shaped and dimensioned to establish stable temperature gradients along said surface.

14. A system according to claim 1, including a sealed chamber positioned below a lowermost point of said vapor discharge pipe, a drain pipe connecting said lowermost point of the vapor discharge pipe with said sealed chamber, and a dynamic pressure take-off connected with said vapor discharge pipe and with an upper point of said chamber, whereby liquid drained into said chamber after a shutdown of the system will be forced back into said vapor discharge pipe by said dynamic pressure when the vapor flow velocity again assumes a value great enough to induce said annular mode of flow.

15. A vaporization cooling system for an electron discharge device comprising:

a boiler containing a body of vaporizable liquid and including a liquid inlet;

an electron discharge device having a heat-dissipating section immersed in said liquid whereby the liquid is partly vaporized during operation of the device; overflow means associated with the boiler to maintain the free surface of said liquid at a constant level; a condenser positioned at an overhead level substantially higher than said constant liquid level; and having an inlet and an outlet;

a liquid feed pipe connected to the outlet of the condenser and connected to the inlet of the boiler; and

a vapor discharge pipe connected to said boiler so as to receive therefrom vapor together with non-vaporized liquid overflowing from said overflow means, said vapor discharge pipe including:

a downgoing leg connected to the boiler; and an upgoing leg having one end connected to said downgoing leg by way of a large-radius connecting section, and having its other end connected to the inlet of said condenser; means to pump to the condenser, by the annular flow effect, the liquid spilled over the overflow means into the vapor discharge pipe by the boiling process comprising:

sufficient amount of liquid in the system so that the height of the column of liquid above the level in the boiler is sufficient to balance the pressure drop through the boiler and the pressure drop required to elevate the water entrained by the annular flow effect, the upgoing leg of the vapor discharge pipe having a flow sectional area small enough to maintain the velocity of the vapor in the upgoing leg at least at the critical velocity for the liquid.

16. A system according to claim 15, wherein said boiler comprises a boiler tank containing said body of liquid, said boiler inlet connects with a bottom point of the boiler tank, and a vapor collecting section overlying the top of said boiler tank, said overflow means being arranged adjacent the top of the tank below said vapor collecting section, said boiler outlet being connected with the boiler tank so as to receive both the vapor from said vapor collecting section and liquid overflowing from said overflow means.

17 A system according to claim 16, wherein said boiler includes an outer jacket surrounding the boiler tank in spaced relation therewith and extending over the top of said tank to provide said vapor collecting section, the

13 top of the boiler tank constitutes an annular overflow means within said outer jacket, and said boiler outlet connects with a bottom point of said outer jacket to receive both vapor from said vapor collecting section and overflowing liquid from said annular overflow means.

18. A system according to claim 17, including vaned annular liquid/vapor separator means between the top of the boiler tank and the vapor collecting section.

'19. A system according to claim 15, including at least one auxiliary heated component associated with the electron discharge device, and wherein said liquid feed pipe is passed in heat transfer relation with said auxiliary component ahead of the connection of said feed pipe with the boiler inlet.

20. A system according to claim 15, wherein said liquid feed pipe and said downgoing leg of the vapor discharge pipe include electrically insulating pipe sections extending from the connections thereof with said boiler inlet and outlet respectively, and said boiler is electrically con- References Cited UNITED STATES PATENTS 2,453,433 11/1948 Hansen et al. 31312 X 2,873,954 2/1959 Protze 313-24 X 3,255,813 6/1966 Besson et al. 165-107 X FOREIGN PATENTS 766,618 1/1957 Great Britain.

ROBERT A. OLEARY, Primary Examiner.

A. W. DAVIS, Assistant Examiner. 

1. A VAPORIZATION SYSTEM COMPRISING: A BOILER HAVING A BODY OF VAPORIZABLE LIQUID THEREIN AND INCLUDING AN INLET FOR FEED LIQUID; A HEAT DISSIPATING SOURCE IN THE BOILER IMMERSED IN SAID LIQUID WHEREBY THE LIQUID IS PARTLY VAPORIZED; OVERFLOW MEANS ASSOCIATED WITH THE BOILER TO MAINTAIN THE FREE SURFACE OF SAID LIQUID AT A CONSTANT LEVEL; AND A RECIRCULATORY FEED SYSTEM FOR SAID LIQUID COMPRISING: A CONDENSER POSITIONED AT AN OVERHEAD LEVEL SUBSTANTIALLY HIGHER THAN SAID CONSTANT LIQUID LEVEL, AND HAVING AN INLET AND AN OUTLET; A LIQUID FEED PIPE CONNECTED TO THE OUTLET OF THE CONDENSER AND CONNECTED TO THE INLET OF THE BOILER; AND A VAPOUR DISCHARGE PIPE CONNECTED TO SAID BOILER SO AS TO RECEIVE THEREFROM VAPOR TOGETHER WITH NON-VAPORIZED LIQUID OVERFLOWING FROM SAID OVERFLOW MEANS, AND INCLUDING AN UPGOING LEG CONNECTED TO THE INLET OF THE CONDENSER; MEANS TO PUMP TO THE CONDENSER, BY THE ANNULAR FLOW EFFECT, THE LIQUID SPILLED OVER THE OVERFLOW MEANS INTO THE VAPOR DISCHARGE PIPE BY THE BOILING PROCESS COMPRISING: SUFFICIENT AMOUNT OF LIQUID IN THE SYSTEM SO THAT THE HEIGHT OF THE COLUMN OF LIQUID ABOVE THE LEVEL IN THE BOILER IS SUFFICIENT TO BALANCE THE PRESSURE DROP THROUGH THE BOILER AND THE PRESSURE DROP REQUIRED TO ELEVATE THE WATER ENTRAINED BY THE ANNULAR FLOW EFFECT, THE UPGOING LEG OF THE VAPOR DISCHARGE PIPE HAVING A FLOW SECTIONAL AREA SMALL ENOUGH TO MAINTAIN THE VELOCITY OF THE VAPOR IN THE UPGOING LEG AT LEAST AT THE CRITICAL VELOCITY FOR THE LIQUID, AND A DOWNGOING LEG CONNECTING WITH THE OVERFLOW MEANS AND WITH SAID UPGOING LEG. 